This invention relates to the field of mass storage devices. More particularly, this invention relates to unlatching the actuator of a disc drive.
One key component of any computer system is a device to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disc drive. The most basic parts of a disc drive are a disc that is rotated, an actuator that moves a transducer to various locations over the disc, and electrical circuitry that is used to write and read data to and from the disc. The disc drive also includes circuitry for encoding and decoding data so that it can be successfully written and retrieved from the disc recording surface. A microprocessor controls most of the operations of the disc drive as well as passing the data and commands between a host computer and the disc drive.
The transducer is typically placed on a small ceramic block, also referred to as a slider, that is aerodynamically designed so that it flies over the disc. The slider is passed over the disc in a transducing relationship with the disc. Most sliders have an air-bearing surface (xe2x80x9cABSxe2x80x9d) that includes rails and a cavity between the rails. When the disc rotates, air is dragged between the rails and the disc surface causing pressure, which forces the head away from the disc. At the same time, the air rushing past the cavity or depression in the air-bearing surface produces a negative pressure area. The negative pressure or suction counteracts the pressure produced at the rails. The slider is also attached to a load spring that produces a force on the slider directed toward the disc surface. The various forces equilibrate so the slider flies over the surface of the disc at a particular desired fly height. The fly height is the distance between the disc surface and the transducing head, which is typically the thickness of the air lubrication film. This film eliminates the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation. In some disc drives, the slider passes through a layer of lubricant rather than flying over the surface of the disc.
Information representative of data is stored on the surface of the storage disc. Disc drive systems read and write information stored on tracks on storage discs. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the storage disc, read and write information on the storage disc after the transducers are accurately positioned over one of the designated tracks on the surface of the storage disc. The transducer is also said to be moved to a target track. As the storage disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the storage disc. Similarly, reading data on a storage disc is accomplished by positioning the read/write head above a target track and reading the stored material on the storage disc. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track. The data is divided into sectors. The sectors are grouped together on the tracks. In some disc drives, the tracks are a multiplicity of concentric circular tracks. In other disc drives, a continuous spiral is one track. Servo feedback information is used to accurately locate the transducer. The actuator assembly is moved to the required position and held very accurately during a read or write operation using the servo information.
When power to the actuator is not present, it is moved to a safe location on the disc, or xe2x80x9cparked.xe2x80x9d Many times a magnetic latch is employed to hold the actuator in the parked position. When the actuator must be moved from the parked position, current disc drives progressively pump or step-increment current to a voice coil motor (VCM) coupled to the actuator, until the actuator produces a force to break the magnetic force used to latch the actuator. After overcoming the magnetic force, movement of the actuator is monitored closely by the servo controller to prevent the actuator from hitting a crash stop generally positioned at the outer periphery of the disc.
Due mainly to the increasing popularity of portable and notebook computers, there is a trend in the industry towards increased non-operating rotational shock requirements. This in turn requires magnetic latches to have greater capacity. In other words the magnetic latch must apply larger amounts of magnetic force. The prior art approaches to unlatching an actuator require a large amount of current to be provided to the VCM to unlatch the actuator; this method is also known as DC unlatch. The amount of current necessary to employ the DC unlatch method is a primary factor in increasing the size and cost of the power amplifier required to produce such a current. There is a strong desire in the industry to reduce the size and cost of disc drives, rather than increase them. Therefore, the DC unlatch method is unacceptable for disc drives intended to have increased non-operational rotational shock requirements.
Another approach is a method called AC unlatch. In this method, the current to the VCM is applied in an alternating direction so as to produce a resonance frequency equal to that of the magnetic latch system.
Most systems or approaches for unlatching the actuator from the latch do not account differences in operating temperature within the disc enclosure. Most systems or approaches for unlatching an actuator presume that the disc drive operates at a substantially fixed operating temperature. There is a possibility that a disc drive will require a longer time to power up or may not power up at all when the operating temperature within the disc drive changes. Another possible effect is that the disc drive may emit audible noise during the various retries during startup. The difference in operating temperature changes the resonant frequency of the bumper that holds the actuator""s latch. For example, in certain disc drives the resonant frequency at a normal operating temperature is approximately 480 Hz. The resonant frequency at a high operating temperature may be approximately 400 Hz, and the resonant frequency at a low operating temperature may be approximately 640 Hz. To release the actuator using resonant frequency, it would be useful to account for the differences in temperature within the disc enclosure and more specifically to account for the differences in resonant frequency of the system given that the actuator will be unlatching at various temperatures.
Therefore, there is a need for a disc drive to account for various operating temperatures during startup. There is also a need for a disc drive to minimize or eliminate the number of retries due to different environmental aspects, such as temperature, within the disc enclosure. And lastly, there is also a need for the drive to unlatch within a minimum amount of time.
The invention includes a disc drive having a base and an actuator assembly attached to the base. The motion and position of the actuator assembly are indetermined by a voice coil which is attached to the actuator assembly. A cover is also attached to the base. The cover and the base form a disc enclosure. The invention also includes a temperature measuring device for indicating the temperature within the disc enclosure and outputting a signal indicating the temperature within the disc enclosure. A current driver applies variable frequency current to the voice coil in response to the signal from the temperature measuring device. The current driver may also apply current having a variable magnitude to the voice coil. The temperature measuring device is located within the disc enclosure. The temperature measuring device may be a thermistor. The disc drive may also include a flex cable having one end attached to the actuator assembly and having the other end attached to electronics associated with the disc drive. The temperature measuring device may be attached to the flex cable.
The current driver is adapted to apply at least two different frequencies of alternating current to the voice coil. The current driver is programmed to attempt to unlatch the actuator assembly at least two times. In some embodiments, the current driver is adapted to apply at least two different frequencies of alternating current, to attempt to unlatch the actuator assembly at least two times, and to change the frequency if at least one attempt has been unsuccessful.
Also disclosed is a method for unlatching an actuator assembly in a disc drive, which includes determining an environmental element near the actuator assembly; and applying a frequency of current to the voice coil in response to the environmental element near the actuator assembly. The method may also vary the magnitude of current to the voice coil in response to the environmental element near the actuator assembly. The environmental element may be the temperature of the environment near the actuator assembly. Applying a frequency of current to the voice coil in response to the environmental element may also include categorizing the temperature into one of at least two categories. A first frequency of current may be applied to a first category of temperature and a second frequency of current may be applied to a second category of temperature. The first frequency of current may be near the resonant frequency of the actuator assembly at a first measured temperature and the second frequency of current may be near the resonant frequency of the actuator assembly at a second measured temperature.
Most generally a disc drive system includes an actuator, an actuator latch for holding the actuator in a latched position when engaged with the actuator, and a device for applying variable frequency current to a voice coil attached to an actuator assembly in response to a measured environmental element near the actuator assembly.
Advantageously, the invention reduces the amount of current necessary to unlatch the actuator. The disc drive accounts for various operating temperatures during the unlatch procedure. The invention minimizes the number of retries due to different environmental aspects, such as temperature, within the disc enclosure. There is also a need for a disc drive unlatches in a minimum amount of time. Advantageously, the invention further decreases the size and cost of the power amplifier required to produce an unlatch current. Additional important features and benefits will become apparent upon a review of the drawings and the corresponding explanation.